Display illumination using a grating

ABSTRACT

A display assembly includes a light source, a spatial light modulator (SLM) and a grating. The light source is configured to emit illumination light, the SLM is configured to receive the illumination light and reflect at least a portion of the illumination light. The grating is positioned to redirect the illumination light output from the light source toward the SLM, receive at least a portion of the reflected light from the SLM, redirect first light having a first polarization toward the light source, and transmit through the grating second light having a second polarization that is orthogonal to the first polarization. Also disclosed are operations performed by the display assembly.

RELATED APPLICATIONS

This application claims the benefit of, and priority to, U.S.Provisional Patent Application Ser. No. 62/898,450, filed Sep. 10, 2019,which is incorporated by reference herein in its entirety. Thisapplication is related to U.S. patent application Ser. No. 16/734,163entitled “Switchable Polarization Retarder Array for Active ZonalIllumination of Display” filed Jan. 3, 2020 and U.S. patent applicationSer. No. 16/734,167 entitled “Display with Switchable Retarder Array”filed Jan. 3, 2020, each of which is hereby incorporated by reference inits entirety.

TECHNICAL FIELD

This relates generally to display devices, and more specifically toilluminators for use in head-mounted display devices.

BACKGROUND

Head-mounted display devices (also called herein head-mounted displays)are gaining popularity as means for providing visual information to auser. For example, the head-mounted display devices are used for virtualreality and augmented reality operations.

Light, compact, and energy-efficient displays are desired inhead-mounted display devices in order to improve a user experience withvirtual reality and augmented reality operations. Additionally, uniformillumination light is desired in order to provide users with highquality images.

SUMMARY

Accordingly, there is a need for compact and lightweight head-mounteddisplay devices with high quality images. Such head-mounted displaydevices will enhance user experience with virtual reality and/oraugmented reality operations.

The above deficiencies and other problems associated with conventionalhead-mounted displays are reduced or eliminated by the disclosed opticalcomponents and display devices.

In accordance with some embodiments, a display assembly includes a lightsource, a reflective spatial light modulator, and a grating. The lightsource is configured to emit illumination light. The reflective spatiallight modulator is configured to receive the illumination light andreflect at least a portion of the illumination light. The grating ispositioned to redirect the illumination light output from the lightsource toward the reflective spatial light modulator, receive at least aportion of the reflected light from the reflective spatial lightmodulator, redirect first light having a first polarization toward thelight source, and transmit second light having a second polarizationthrough the grating. The second polarization is orthogonal to the firstpolarization.

In accordance with some embodiments, a method includes receivingillumination light at a grating and redirecting, with the grating, theillumination light toward a reflective spatial light modulator. In someembodiments, the illumination light has a first polarization. The methodalso includes receiving the illumination light redirected by the gratingat the reflective spatial light modulator and providing, by thereflective spatial light modulator, first light having firstpolarization and second light having a second polarization that isorthogonal to the first polarization. The method further includesreceiving the first light and the second light at the grating;directing, with the grating, the first light toward a first direction;and directing the second light toward a second direction that isdifferent from the first direction.

Thus, the disclosed embodiments provide lightweight and compact displaydevices that provide uniform illumination and high quality images. Insome embodiments, the display devices are head-mounted display devices.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the various described embodiments,reference should be made to the Description of Embodiments below, inconjunction with the following drawings in which like reference numeralsrefer to corresponding parts throughout the figures.

FIG. 1 is a perspective view of a display device in accordance with someembodiments.

FIG. 2 is a block diagram of a system including a display device inaccordance with some embodiments.

FIG. 3 is an isometric view of a display device in accordance with someembodiments.

FIGS. 4A-4B are schematic diagrams illustrating a display assembly inaccordance with some embodiments.

FIGS. 4C-4D are schematic diagrams illustrating a reflective spatiallight modulator in accordance with some embodiments.

FIGS. 5A-5B illustrate a flow diagram illustrating a method of using agrating in accordance with some embodiments.

These figures are not drawn to scale unless indicated otherwise.

DETAILED DESCRIPTION

There is a need for head-mounted display devices that are lightweight,compact, and can provide uniform illumination.

The present disclosure provides display devices that include a gratingconfigured to direct illumination light emitted from a light sourcetoward a reflective spatial light modulator and selectively direct lightoutput from the reflective spatial light modulator for delivery to auser's eye. Such display devices have a compact footprint, therebyenabling reduction of the size and weight of display devices. Inaddition, such display devices provide uniform illumination, therebyimproving the image quality when a reflective display element (e.g., areflective spatial light modulator) is used.

Reference will now be made to embodiments, examples of which areillustrated in the accompanying drawings. In the following description,numerous specific details are set forth in order to provide anunderstanding of the various described embodiments. However, it will beapparent to one of ordinary skill in the art that the various describedembodiments may be practiced without these specific details. In otherinstances, well-known methods, procedures, components, circuits, andnetworks have not been described in detail so as not to unnecessarilyobscure aspects of the embodiments.

It will also be understood that, although the terms first, second, etc.are, in some instances, used herein to describe various elements, theseelements should not be limited by these terms. These terms are used onlyto distinguish one element from another. For example, a first reflectorcould be termed a second reflector, and, similarly, a second reflectorcould be termed a first reflector, without departing from the scope ofthe various described embodiments. The first reflector and the secondreflector are both light reflectors, but they are not the samereflector.

The terminology used in the description of the various describedembodiments herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used in thedescription of the various described embodiments and the appendedclaims, the singular forms “a,” “an,” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will also be understood that the term “and/or” as usedherein refers to and encompasses any and all possible combinations ofone or more of the associated listed items. It will be furtherunderstood that the terms “includes,” “including,” “comprises,” and/or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. The term “exemplary” is used herein in the senseof “serving as an example, instance, or illustration” and not in thesense of “representing the best of its kind.”

FIG. 1 illustrates display device 100 in accordance with someembodiments. In some embodiments, display device 100 is configured to beworn on a head of a user (e.g., by having the form of spectacles oreyeglasses, as shown in FIG. 1) or to be included as part of a helmetthat is to be worn by the user. When display device 100 is configured tobe worn on a head of a user or to be included as part of a helmet,display device 100 is called a head-mounted display. Alternatively,display device 100 is configured for placement in proximity of an eye oreyes of the user at a fixed location, without being head-mounted (e.g.,display device 100 is mounted in a vehicle, such as a car or anairplane, for placement in front of an eye or eyes of the user). Asshown in FIG. 1, display device 100 includes display 110. Display 110 isconfigured for presenting visual contents (e.g., augmented realitycontents, virtual reality contents, mixed reality contents, or anycombination thereof) to a user.

In some embodiments, display device 100 includes one or more componentsdescribed herein with respect to FIG. 2. In some embodiments, displaydevice 100 includes additional components not shown in FIG. 2.

FIG. 2 is a block diagram of system 200 in accordance with someembodiments. The system 200 shown in FIG. 2 includes display device 205(which corresponds to display device 100 shown in FIG. 1), imagingdevice 235, and input interface 240 that are each coupled to console210. While FIG. 2 shows an example of system 200 including displaydevice 205, imaging device 235, and input interface 240, in otherembodiments, any number of these components may be included in system200. For example, there may be multiple display devices 205 each havingassociated input interface 240 and being monitored by one or moreimaging devices 235, with each display device 205, input interface 240,and imaging devices 235 communicating with console 210. In alternativeconfigurations, different and/or additional components may be includedin system 200. For example, in some embodiments, console 210 isconnected via a network (e.g., the Internet) to system 200 or isself-contained as part of display device 205 (e.g., physically locatedinside display device 205). In some embodiments, display device 205 isused to create mixed reality by adding in a view of the realsurroundings. Thus, display device 205 and system 200 described here candeliver augmented reality, virtual reality, and mixed reality.

In some embodiments, as shown in FIG. 1, display device 205 correspondsto display device 100 and is a head-mounted display that presents mediato a user. Examples of media presented by display device 205 include oneor more images, video, audio, or some combination thereof. In someembodiments, audio is presented via an external device (e.g., speakersand/or headphones) that receives audio information from display device205, console 210, or both, and presents audio data based on the audioinformation. In some embodiments, display device 205 immerses a user inan augmented environment.

In some embodiments, display device 205 also acts as an augmentedreality (AR) headset. In these embodiments, display device 205 augmentsviews of a physical, real-world environment with computer-generatedelements (e.g., images, video, sound, etc.). Moreover, in someembodiments, display device 205 is able to cycle between different typesof operation. Thus, display device 205 operate as a virtual reality (VR)device, an augmented reality (AR) device, as glasses or some combinationthereof (e.g., glasses with no optical correction, glasses opticallycorrected for the user, sunglasses, or some combination thereof) basedon instructions from application engine 255.

Display device 205 includes electronic display 215, one or moreprocessors 216, eye tracking module 217, adjustment module 218, one ormore locators 220, one or more position sensors 225, one or moreposition cameras 222, memory 228, inertial measurement unit (IMU) 230,one or more optical assemblies 260, or a subset or superset thereof(e.g., display device 205 with electronic display 215, optical assembly260, without any other listed components). Some embodiments of displaydevice 205 have different modules than those described here. Similarly,the functions can be distributed among the modules in a different mannerthan is described here.

One or more processors 216 (e.g., processing units or cores) executeinstructions stored in memory 228. Memory 228 includes high-speed randomaccess memory, such as DRAM, SRAM, DDR RAM or other random access solidstate memory devices; and may include non-volatile memory, such as oneor more magnetic disk storage devices, optical disk storage devices,flash memory devices, or other non-volatile solid state storage devices.Memory 228, or alternately the non-volatile memory device(s) withinmemory 228, includes a non-transitory computer readable storage medium.In some embodiments, memory 228 or the computer readable storage mediumof memory 228 stores programs, modules and data structures, and/orinstructions for displaying one or more images on electronic display215.

Electronic display 215 displays images to the user in accordance withdata received from console 210 and/or processor(s) 216. In variousembodiments, electronic display 215 may comprise a single adjustabledisplay element or multiple adjustable display elements (e.g., a displayfor each eye of a user). In some embodiments, electronic display 215 isconfigured to project images to the user through one or more opticalassemblies 260.

In some embodiments, the display element includes one or more lightemission devices and a corresponding array of spatial light modulators.A spatial light modulator is an array of electro-optic pixels,opto-electronic pixels, some other array of devices that dynamicallyadjust the amount of light transmitted by each device, or somecombination thereof. These pixels are placed behind one or more lenses.In some embodiments, the spatial light modulator is an array of liquidcrystal based pixels in an LCD (a Liquid Crystal Display). Examples ofthe light emission devices include: an organic light emitting diode, anactive-matrix organic light-emitting diode, a light emitting diode, sometype of device capable of being placed in a flexible display, or somecombination thereof. The light emission devices include devices that arecapable of generating visible light (e.g., red, green, blue, etc.) usedfor image generation. The spatial light modulator is configured toselectively attenuate individual light emission devices, groups of lightemission devices, or some combination thereof. Alternatively, when thelight emission devices are configured to selectively attenuateindividual emission devices and/or groups of light emission devices, thedisplay element includes an array of such light emission devices withouta separate emission intensity array.

One or more optical components in the one or more optical assemblies 260direct light from the arrays of light emission devices (optionallythrough the emission intensity arrays) to locations within each eyeboxand ultimately to the back of the user's retina(s). An eyebox is aregion that is occupied by an eye of a user of display device 205 (e.g.,a user wearing display device 205) who is viewing images from displaydevice 205. In some cases, the eyebox is represented as a 10 mm×10 mmsquare. In some embodiments, the one or more optical components includeone or more coatings, such as anti-reflective coatings, and one or morepolarization volume holograms (PVH).

In some embodiments, the display element includes an infrared (IR)detector array that detects IR light that is retro-reflected from theretinas of a viewing user, from the surface of the corneas, lenses ofthe eyes, or some combination thereof. The IR detector array includes anIR sensor or a plurality of IR sensors that each correspond to adifferent position of a pupil of the viewing user's eye. In alternateembodiments, other eye tracking systems may also be employed.

Eye tracking module 217 determines locations of each pupil of a user'seyes. In some embodiments, eye tracking module 217 instructs electronicdisplay 215 to illuminate the eyebox with IR light (e.g., via IRemission devices in the display element).

A portion of the emitted IR light will pass through the viewing user'spupil and be retro-reflected from the retina toward the IR detectorarray, which is used for determining the location of the pupil.Additionally or alternatively, the reflection off of the surfaces of theeye is used to also determine location of the pupil. In some cases, theIR detector array scans for retro-reflection and identifies which IRemission devices are active when retro-reflection is detected. Eyetracking module 217 may use a tracking lookup table and the identifiedIR emission devices to determine the pupil locations for each eye. Thetracking lookup table maps the received signals on the IR detector arrayto locations (corresponding to pupil locations) in each eyebox. In someembodiments, the tracking lookup table is generated via a calibrationprocedure (e.g., user looks at various known reference points in animage and eye tracking module 217 maps the locations of the user's pupilwhile looking at the reference points to corresponding signals receivedon the IR tracking array). As mentioned above, in some embodiments,system 200 may use other eye tracking systems than the embedded IR eyetracking system described herein.

Adjustment module 218 generates an image frame based on the determinedlocations of the pupils. In some embodiments, this sends a discreteimage to the display that will tile sub-images together thus a coherentstitched image will appear on the back of the retina. Adjustment module218 adjusts an output (i.e. the generated image frame) of electronicdisplay 215 based on the detected locations of the pupils. Adjustmentmodule 218 instructs portions of electronic display 215 to pass imagelight to the determined locations of the pupils. In some embodiments,adjustment module 218 also instructs the electronic display not toprovide image light to positions other than the determined locations ofthe pupils. Adjustment module 218 may, for example, block and/or stoplight emission devices whose image light falls outside of the determinedpupil locations, allow other light emission devices to emit image lightthat falls within the determined pupil locations, translate and/orrotate one or more display elements, dynamically adjust curvature and/orrefractive power of one or more active lenses in the lens (e.g.,microlens) arrays, or some combination thereof.

Optional locators 220 are objects located in specific positions ondisplay device 205 relative to one another and relative to a specificreference point on display device 205. A locator 220 may be a lightemitting diode (LED), a corner cube reflector, a reflective marker, atype of light source that contrasts with an environment in which displaydevice 205 operates, or some combination thereof. In embodiments wherelocators 220 are active (i.e., an LED or other type of light emittingdevice), locators 220 may emit light in the visible band (e.g., about400 nm to 750 nm), in the infrared band (e.g., about 750 nm to 1 mm), inthe ultraviolet band (about 100 nm to 400 nm), some other portion of theelectromagnetic spectrum, or some combination thereof.

In some embodiments, locators 220 are located beneath an outer surfaceof display device 205, which is transparent to the wavelengths of lightemitted or reflected by locators 220 or is thin enough to notsubstantially attenuate the wavelengths of light emitted or reflected bylocators 220. Additionally, in some embodiments, the outer surface orother portions of display device 205 are opaque in the visible band ofwavelengths of light. Thus, locators 220 may emit light in the IR bandunder an outer surface that is transparent in the IR band but opaque inthe visible band.

IMU 230 is an electronic device that generates calibration data based onmeasurement signals received from one or more position sensors 225.Position sensor 225 generates one or more measurement signals inresponse to motion of display device 205. Examples of position sensors225 include: one or more accelerometers, one or more gyroscopes, one ormore magnetometers, another suitable type of sensor that detects motion,a type of sensor used for error correction of IMU 230, or somecombination thereof. Position sensors 225 may be located external to IMU230, internal to IMU 230, or some combination thereof.

Based on the one or more measurement signals from one or more positionsensors 225, IMU 230 generates first calibration data indicating anestimated position of display device 205 relative to an initial positionof display device 205. For example, position sensors 225 includemultiple accelerometers to measure translational motion (forward/back,up/down, left/right) and multiple gyroscopes to measure rotationalmotion (e.g., pitch, yaw, roll). In some embodiments, IMU 230 rapidlysamples the measurement signals and calculates the estimated position ofdisplay device 205 from the sampled data. For example, IMU 230integrates the measurement signals received from the accelerometers overtime to estimate a velocity vector and integrates the velocity vectorover time to determine an estimated position of a reference point ondisplay device 205. Alternatively, IMU 230 provides the sampledmeasurement signals to console 210, which determines the firstcalibration data. The reference point is a point that may be used todescribe the position of display device 205. While the reference pointmay generally be defined as a point in space; however, in practice thereference point is defined as a point within display device 205 (e.g., acenter of IMU 230).

In some embodiments, IMU 230 receives one or more calibration parametersfrom console 210. As further discussed below, the one or morecalibration parameters are used to maintain tracking of display device205. Based on a received calibration parameter, IMU 230 may adjust oneor more IMU parameters (e.g., sample rate). In some embodiments, certaincalibration parameters cause IMU 230 to update an initial position ofthe reference point so it corresponds to a next calibrated position ofthe reference point. Updating the initial position of the referencepoint as the next calibrated position of the reference point helpsreduce accumulated error associated with the determined estimatedposition. The accumulated error, also referred to as drift error, causesthe estimated position of the reference point to “drift” away from theactual position of the reference point over time.

Imaging device 235 generates calibration data in accordance withcalibration parameters received from console 210. Calibration dataincludes one or more images showing observed positions of locators 220that are detectable by imaging device 235. In some embodiments, imagingdevice 235 includes one or more still cameras, one or more videocameras, any other device capable of capturing images including one ormore locators 220, or some combination thereof. Additionally, imagingdevice 235 may include one or more filters (e.g., used to increasesignal to noise ratio). Imaging device 235 is configured to optionallydetect light emitted or reflected from locators 220 in a field of viewof imaging device 235. In embodiments where locators 220 include passiveelements (e.g., a retroreflector), imaging device 235 may include alight source that illuminates some or all of locators 220, whichretro-reflect the light toward the light source in imaging device 235.Second calibration data is communicated from imaging device 235 toconsole 210, and imaging device 235 receives one or more calibrationparameters from console 210 to adjust one or more imaging parameters(e.g., focal length, focus, frame rate, ISO, sensor temperature, shutterspeed, aperture, etc.).

In some embodiments, display device 205 includes one or more opticalassemblies 260. In some embodiments, display device 205 optionallyincludes a single optical assembly 260 or multiple optical assemblies260 (e.g., an optical assembly 260 for each eye of a user). In someembodiments, the one or more optical assemblies 260 receive image lightfor the computer generated images from the electronic display device(s)215 and direct the image light toward an eye or eyes of a user. Thecomputer-generated images include still images, animated images, and/ora combination thereof. The computer-generated images include objectsthat appear to be two-dimensional and/or three-dimensional objects.

In some embodiments, electronic display device 215 projectscomputer-generated images to one or more reflective elements (notshown), and the one or more optical assemblies receive the image lightfrom the one or more reflective elements and direct the image light tothe eye(s) of the user. In some embodiments, the one or more reflectiveelements are partially transparent (e.g., the one or more reflectiveelements have a transmittance of at least 15%, 20%, 25%, 30%, 35%, 40%,45%, or 50%), which allows transmission of ambient light. In suchembodiments, computer-generated images projected by electronic display215 are superimposed with the transmitted ambient light (e.g.,transmitted ambient image) to provide augmented reality images.

Input interface 240 is a device that allows a user to send actionrequests to console 210. An action request is a request to perform aparticular action. For example, an action request may be to start or endan application or to perform a particular action within the application.Input interface 240 may include one or more input devices. Example inputdevices include: a keyboard, a mouse, a game controller, data from brainsignals, data from other parts of the human body, or any other suitabledevice for receiving action requests and communicating the receivedaction requests to console 210. An action request received by inputinterface 240 is communicated to console 210, which performs an actioncorresponding to the action request. In some embodiments, inputinterface 240 may provide haptic feedback to the user in accordance withinstructions received from console 210. For example, haptic feedback isprovided when an action request is received, or console 210 communicatesinstructions to input interface 240 causing input interface 240 togenerate haptic feedback when console 210 performs an action.

Console 210 provides media to display device 205 for presentation to theuser in accordance with information received from one or more of:imaging device 235, display device 205, and input interface 240. In theexample shown in FIG. 2, console 210 includes application store 245,tracking module 250, and application engine 255. Some embodiments ofconsole 210 have different modules than those described in conjunctionwith FIG. 2. Similarly, the functions further described herein may bedistributed among components of console 210 in a different manner thanis described here.

When application store 245 is included in console 210, application store245 stores one or more applications for execution by console 210. Anapplication is a group of instructions, that when executed by aprocessor, is used for generating content for presentation to the user.Content generated by the processor based on an application may be inresponse to inputs received from the user via movement of display device205 or input interface 240. Examples of applications include: gamingapplications, conferencing applications, video playback application, orother suitable applications.

When tracking module 250 is included in console 210, tracking module 250calibrates system 200 using one or more calibration parameters and mayadjust one or more calibration parameters to reduce error indetermination of the position of display device 205. For example,tracking module 250 adjusts the focus of imaging device 235 to obtain amore accurate position for observed locators on display device 205.Moreover, calibration performed by tracking module 250 also accounts forinformation received from IMU 230. Additionally, if tracking of displaydevice 205 is lost (e.g., imaging device 235 loses line of sight of atleast a threshold number of locators 220), tracking module 250re-calibrates some or all of system 200.

In some embodiments, tracking module 250 tracks movements of displaydevice 205 using second calibration data from imaging device 235. Forexample, tracking module 250 determines positions of a reference pointof display device 205 using observed locators from the secondcalibration data and a model of display device 205. In some embodiments,tracking module 250 also determines positions of a reference point ofdisplay device 205 using position information from the first calibrationdata. Additionally, in some embodiments, tracking module 250 may useportions of the first calibration data, the second calibration data, orsome combination thereof, to predict a future location of display device205. Tracking module 250 provides the estimated or predicted futureposition of display device 205 to application engine 255.

Application engine 255 executes applications within system 200 andreceives position information, acceleration information, velocityinformation, predicted future positions, or some combination thereof ofdisplay device 205 from tracking module 250. Based on the receivedinformation, application engine 255 determines content to provide todisplay device 205 for presentation to the user. For example, if thereceived information indicates that the user has looked to the left,application engine 255 generates content for display device 205 thatmirrors the user's movement in an augmented environment. Additionally,application engine 255 performs an action within an applicationexecuting on console 210 in response to an action request received frominput interface 240 and provides feedback to the user that the actionwas performed. The provided feedback may be visual or audible feedbackvia display device 205 or haptic feedback via input interface 240.

FIG. 3 is an isometric view of display device 300 in accordance withsome embodiments. In some other embodiments, display device 300 is partof some other electronic display (e.g., a digital microscope, ahead-mounted display device, etc.). In some embodiments, display device300 includes light emission device 310 and an optical assembly 330,which may include one or more lenses and/or other optical components. Insome embodiments, display device 300 also includes an IR detector array.

Light emission device 310 emits image light and optional IR light towardthe viewing user. Light emission device 310 includes one or more lightemission components that emit light in the visible light (and optionallyincludes components that emit light in the IR). Light emission device310 may include, e.g., an array of LEDs, an array of microLEDs, an arrayof OLEDs, or some combination thereof.

In some embodiments, light emission device 310 includes an emissionintensity array (e.g., a spatial light modulator) configured toselectively attenuate light emitted from light emission device 310. Insome embodiments, the emission intensity array is composed of aplurality of liquid crystal cells or pixels, groups of light emissiondevices, or some combination thereof. Each of the liquid crystal cellsis, or in some embodiments, groups of liquid crystal cells are,addressable to have specific levels of attenuation. For example, at agiven time, some of the liquid crystal cells may be set to noattenuation, while other liquid crystal cells may be set to maximumattenuation. In this manner, the emission intensity array is able toprovide image light and/or control what portion of the image light ispassed to the optical assembly 330. In some embodiments, display device300 uses the emission intensity array to facilitate providing imagelight to a location of pupil 350 of eye 340 of a user, and minimize theamount of image light provided to other areas in the eyebox.

The optical assembly 330 includes one or more lenses. The one or morelenses in optical assembly 330 receive modified image light (e.g.,attenuated light) from light emission device 310, and direct themodified image light to a location of pupil 350. The optical assembly330 may include additional optical components, such as color filters,mirrors, etc.

An optional IR detector array detects IR light that has beenretro-reflected from the retina of eye 340, a cornea of eye 340, acrystalline lens of eye 340, or some combination thereof. The IRdetector array includes either a single IR sensor or a plurality of IRsensitive detectors (e.g., photodiodes). In some embodiments, the IRdetector array is separate from light emission device array 310. In someembodiments, the IR detector array is integrated into light emissiondevice array 310.

In some embodiments, light emission device 310 including an emissionintensity array make up a display element. Alternatively, the displayelement includes light emission device 310 (e.g., when light emissiondevice array 310 includes individually adjustable pixels) without theemission intensity array. In some embodiments, the display elementadditionally includes the IR array. In some embodiments, in response toa determined location of pupil 350, the display element adjusts theemitted image light so that the light output by the display element isrefracted by one or more lenses toward the determined location of pupil350, and not toward other locations in the eyebox.

In some embodiments, display device 300 includes one or more broadbandsources (e.g., one or more white LEDs) coupled with a plurality of colorfilters, in addition to, or instead of, light emission device 310.

In some embodiments, display device 300 (or light emission device 310 ofdisplay device 300) includes a reflective spatial light modulator, suchas a Liquid Crystal on Silicon (LCoS) spatial light modulator. In someembodiments, the LCoS spatial light modulator includes liquid crystals.In some embodiments, the LCoS spatial light modulator includesferroelectric liquid crystals. The reflective spatial light modulatorhas an array of pixels (or subpixels), and a respective pixel (or arespective subpixel) is individually controlled to reflect lightimpinging thereon (e.g., a pixel is activated to reflect light impingingthereon or deactivated to cease reflecting the light impinging thereon)or modulate the reflected light (e.g., a pixel is activated to changethe polarization of the reflected light or deactivated to cease changingthe polarization of the reflected light, or vice versa). In someembodiments, display device 300 includes multiple reflective spatiallight modulators (e.g., a first reflective spatial light modulator for afirst color, such as red, a second reflective spatial light modulatorfor a second color, such as green, and a third reflective spatial lightmodulator for a third color, such as blue). Such reflective spatiallight modulator requires an illuminator that provides light to thereflective spatial light modulator.

Conventional illuminators (e.g., conventional LCoS illuminators) use asingle polarizing beam splitter (PBS), which has a height thatcorresponds to a width of the reflective spatial light modulator (e.g.,an LCoS spatial light modulator), for illuminating the LCoS spatiallight modulators. This increases the required volume of the illuminator.In addition, as the LCoS spatial light modulator typically reflects aportion of illumination light to provide image light, non-uniformity inthe illumination light will lead to non-uniformity in the image light.Thus, there is a need for compact illuminators that can provide uniformillumination of LCoS spatial light modulators.

FIGS. 4A and 4B are schematic diagrams illustrating a display assembly400 in accordance with some embodiments. Display assembly 400 enablescompact illumination, while improving uniformity in illumination light.Display assembly 400 includes a reflective spatial light modulator 430,such as an LCoS spatial light modulator, and optical devices used toilluminate the reflective spatial light modulator. In some embodiments,the reflective spatial light modulator is integrated with such opticaldevice.

As shown, display assembly 400 also includes a light source 410 and agrating 420. The grating 420 is positioned so that a surface 420-1 or420-2 (e.g., an optical surface 420-1 or 420-2) of the grating 420 formsan angle θ with respect to a surface 430-1 or 430-2 of the reflectivespatial light modulator 430 (e.g., a surface 420-1 or 420-2 of thegrating 420 is non-parallel and non-perpendicular with respect to asurface 430-1 or 430-2 of the reflective spatial light modulator 430).The light source 410 is configured (e.g., positioned) to outputillumination light 490 toward the grating 420. In some embodiments, thegrating 420 is a polarization-dependent grating. The grating 420 isconfigured (e.g., positioned) to receive illumination light 490 having afirst polarization (e.g., a first linear polarization, such ass-polarization) and to redirect (e.g., diffract) the illumination light490 light having the first polarization toward the reflective spatiallight modulator 430. The reflective spatial light modulator 430 includesa plurality of pixels 431-1, 431-2, 431-3, . . . , 431-n, referred toindividually or collectively as pixel 431. A respective pixel 431 of theplurality of pixels is configured to receive the illumination light 490,which has a first polarization, and provide: (i) first light 492-1having the first polarization while the respective pixel 431 is in afirst state (shown in FIG. 4A) and (ii) second light 492-2 having asecond polarization (e.g., a second linear polarization, such asp-polarization) while the respective pixel 431 is in a second state thatis different from the first state (shown in FIG. 4B). For example, therespective pixel 431 may provide the first light having the samepolarization (e.g., the first polarization) as the illumination lightwhile the respective pixel 431 is deactivated (e.g., turned off) andprovide the second light having a polarization different from (e.g.,orthogonal to) the polarization of the illumination light while therespective pixel 431 is activated (e.g., turned on). Alternatively, therespective pixel 431 may provide the first light having the samepolarization as the illumination light while the respective pixel 431 isactivated (e.g., turned on), and provide the second light having apolarization different from the polarization of the illumination lightwhile the respective pixel 431 is deactivated (e.g., turned off). Insome embodiments, the second polarization is orthogonal to the firstpolarization. The grating 420 is further configured to receive the firstlight 492-1 (shown in FIG. 4A) or the second light 492-2 (shown in FIG.4B) output from the reflective spatial light modulator 430. The grating420 is configured to redirect (e.g., diffract) the first light 492-1having the first polarization toward the light source 410 (shown in FIG.4A as light 494) and to transmit (e.g., to a zeroth order diffractiondirection of the grating 420) the second light 492-2 having the secondpolarization (shown in FIG. 4B as light 496-2). In some embodiments, thegrating 420 is configured to redirect light having the firstpolarization, including the at least a portion of illumination light 490(e.g., via zeroth order reflection) as light 496-1 and at least aportion of the first light 492-1 (e.g., via zeroth order transmission)as the light 496-2, toward a same first diffraction order direction ofthe grating 420. In some embodiments, the grating 420 is configured totransmit or redirect (e.g., diffract) light without changing apolarization of the transmitted or redirected (e.g., diffracted) light.

As shown in FIGS. 4A-4B, display assembly 400 allows physical separationof light having different polarizations, which, in turn, improves theextinction ratio of display assembly 400.

In some embodiments, the grating 420 is an isotropic grating thatincludes an isotropic material.

In some embodiments, display assembly 400 further includes an outputassembly 470 configured to direct the second light 492-2 (e.g.,propagate light via total internal reflection) toward an eye 340 of auser. In such cases, the second light 492-2 is transmitted through thegrating 420 toward the output assembly. In some embodiments, the outputassembly 470 includes a waveguide and an in-coupler so that at least aportion of the second light 492-2 is coupled into the waveguide.

In some embodiments, display assembly 400 further includes a transparentoptical element 440 (e.g., prism) that has a first surface 440-1 and asecond surface 440-2. The second surface 440-2 is non-parallel to thefirst surface 440-1. In some embodiments, the second surface 440-2 isparallel to a surface of the reflective spatial light modulator 430. Thegrating 420 is disposed on the first surface 440-1 of the transparentoptical element 440. As shown in FIG. 4A, the transparent opticalelement 440 is disposed between the grating 420 and the reflectivespatial light modulator 430, and transparent optical element 440 has arefractive index that is different from the refractive index of air. Insome embodiments, the refractive index of the transparent opticalelement 440 in combination with the angle θ between a surface 420-1 (orsurface 420-2) of the grating 420 and a surface 430-1 (or surface 430-2)of the reflective spatial light modulator 430 determines the first andsecond directions (e.g., the directions of the first diffraction orderand the zeroth diffraction order, respectively). For example, as shownin FIG. 4B, the second light 492-2 is transmitted through the grating420 into the direction of the zeroth order diffraction and is furtherrefracted at the first surface 440-1 of the transparent optical element440 based on the refractive index of the transparent optical element 440and the incident angle of the second light 492-2 onto the first surface440-1.

In some embodiments, display assembly 400 further includes a polarizer450 (e.g., an absorptive polarizer) that is disposed between the lightsource 410 and the grating 420. For example, the light source 410 mayoutput initial light 489 toward the polarizer 450. The initial light 489may include light having the first polarization as well as light havingother polarizations that are different from the first polarization(e.g., light having a polarization that is orthogonal to the firstpolarization). In some cases, the initial light 489 may be unpolarized.The polarizer 450 is configured to transmit light having the firstpolarization and block transmission of light having the secondpolarization. Thus, the polarizer 450, when included in display assembly400, ensures that illumination light 490, received by the grating 420,has substantially the first polarization (e.g., a light source thatprovides initial light 489 having random polarization may be used inconjunction with the polarizer 450 so that only light having the firstpolarization is provided to the grating 420).

In some embodiments, the polarizer 450 is a reflective polarizer.

In some embodiments, display assembly 400 further includes a polarizer460. In some embodiments, the polarizer 460 is disposed between thegrating 420 and the output assembly 470 when the output assembly 470 isincluded. The polarizer 460 is configured to transmit light having thesecond polarization and block transmission of light having the firstpolarization. Thus, as shown in Figured 4B, the second light 492-2having the second polarization is transmitted through the polarizer 460.Additionally, as shown in FIG. 4A, any portion of the first light 492-1,having the first polarization, that may not be successfully directed bythe grating 420 (e.g., zeroth order leakage, such as light 496-1, whichcorresponds to the zeroth order reflection of the illumination light490, and light 496-2, which corresponds to the zeroth order transmissionof the first light 492-1 having the first polarization), is blocked bypolarizer 460 from being transmitted towards the output assembly (whenincluded). The polarizer 460 may be any of: a reflective polarizer(e.g., an optical element that reflects light having the firstpolarization and transmits light having the second polarization) or anabsorptive polarizer (e.g., an optical element that absorbs light havingthe first polarization and transmits light having the secondpolarization).

FIGS. 4C and 4D are schematic diagram illustrating a reflective spatiallight modulator 430 in accordance with some embodiments. In someembodiments, as shown in FIG. 4C, the reflective spatial light modulator430 includes a reflective surface 432 (e.g., a mirror or a reflector,such as a full reflector), an optical retarder 433 (e.g., quarter waveplate), and a layer of optically anisotropic molecules 434 (e.g., liquidcrystals) that are disposed between the reflective surface 432 and theoptical retarder 433. Additionally, the reflective spatial lightmodulator 430 may include one or more transistors 435 and an opticallytransparent electrode 438 so that an electric field applied to arespective portion of the layer of optically anisotropic molecules 434can be individually controlled. In some embodiments, the one or moretransistors 435 are integrated with a substrate 437 that may include asilicon substrate and/or a printed circuit board (PCB). In someembodiments, the one or more transistors may be ametal-oxide-semiconductor field-effect transistor (e.g., MOSFET). Insome embodiments, the transistors are arranged in a complementarymetal-oxide-semiconductor (e.g., CMOS) configuration.

The layer of optically anisotropic molecules 434 is disposed between theoptically transparent electrode 438 and the one or more transistors 435.Each transistor of the one or more transistors 435 defines a pixel 431and a respective transistor 435 is configured to control a state of arespective pixel 431. This configuration allows polarization modulation.For example, the respective pixel 431 of the plurality of pixels mayprovide the first light having the same polarization as the illuminationlight while the respective pixel 431 (or a corresponding transistor 435)is in the first state and provide the second light having a polarizationdifferent from (e.g., orthogonal to) the polarization of theillumination light while the respective pixel 431 (or the correspondingtransistor 435) is the second state. Thus, in some embodiments, arespective pixel 431 of the plurality of pixels is individuallyactivatable. For example, the respective pixel 431 of the plurality ofpixels may be activated or deactivated independent of whether the restof the plurality of pixels are activated or deactivated. Similarly, arespective transistor of the plurality of transistors 435 may beindividually activatable.

In some embodiments, an electrical signal applied at each pixel 431 isindividually controllable via the one or more transistors 435. Forexample, a respective pixel 431 is in the first state when a respectivetransistor 435 allows an electrical signal to be applied at a respectivepixel 431 so that optically anisotropic molecules in a portion of thelayer of optically anisotropic molecules that are located adjacent tothe respective transistor 435 have a first orientation, and therespective pixel 431 is in the second state when the respectivetransistor 435 does not allow an electrical signal to reach therespective pixel 431 so that the optically anisotropic molecules in theportion of the layer of optically anisotropic molecules that are locatedadjacent to the respective transistor 435 have a second orientation thatis different from the first orientation, or vice versa. For example, asshown in FIG. 4D, a first pixel 431-1 is in a first state and the secondpixel 431-2 is in the second state. An electrical signal is applied(e.g., “on”) at the first pixel 431-1, and optically anisotropicmolecules (e.g., liquid crystals) that are in a first portion of thelayer of optically anisotropic molecules, located adjacent to a firsttransistor 435-1 and corresponding to the first pixel 431-1, have afirst orientation. An electrical signal is not applied (e.g., “off”) ata second pixel 431-2, and optically anisotropic molecules that are in asecond portion of the layer of optically anisotropic molecules, locatedadjacent to a second transistor 435-2 and corresponding to the secondpixel 431-2, have a second orientation that is different from (in somecases, orthogonal to), the first orientation. In some embodiments, thefirst transistor 435-1 may be connected to a different electrical source(e.g., voltage or current source) than the second transistor 435-2.Alternatively, the first transistor 435-1 and the second transistor435-2 may be connected in parallel to a same electrical source.Substrate 437 and optical retarder 433 are not shown in FIG. 4D so asnot to obscure other aspects of the reflective spatial light modulator430.

In some embodiments, the reflective spatial light modulator 430 alsoincludes an alignment layer 436 disposed adjacent to the layer ofoptically anisotropic molecules 434 (e.g., liquid crystals). In someembodiments, the layer of optically anisotropic molecules 434 isdisposed between the one or more transistors 435 and the alignment layer436. In some embodiments, the layer of optically anisotropic molecules434 is in contact with the alignment layer 436.

FIGS. 5A-5B illustrate a flow diagram illustrating a method 500 inaccordance with some embodiments. The method 500 includes (operation510) receiving illumination light 490 at a grating 420 and (operation520) redirecting (e.g., diffracting), with the grating 420, theillumination light 490 toward a reflective spatial light modulator 430that includes a plurality of pixels 431. In some embodiments, theillumination light 490 has a first polarization. The method 500 alsoincludes (operation 530) receiving, at the reflective spatial lightmodulator 430, the illumination light 490 redirected by the grating 420.The method 500 further includes (operation 540) providing, by thereflective spatial light modulator 430, first light 492-1 having a firstpolarization and second light 492-2 having a second polarization that isorthogonal to the first polarization. The method 500 further includes(operation 550) receiving the first light 492-1 and the second light492-2 at the grating 420 and (operation 560) directing, with the grating420, the first light 492-1 toward a first direction and directing, withthe grating 420, the second light 492-2 toward a second direction thatis different from the first direction.

In some embodiments, the method 500 includes (operation 502) outputtinginitial light (e.g., initial light 489) from a light source 410;receiving the initial light at an absorptive polarizer (e.g., polarizer450); and transmitting, through the absorptive polarizer (e.g.,polarizer 450), at least a portion of the initial light having the firstpolarization as the illumination light 490.

In some embodiments, the method 500 includes (operation 504) outputtingthe illumination light 490 from a light source 410 and the grating 420is disposed between the light source 410 and the reflective spatiallight modulator 430.

In some embodiments, the reflective spatial light modulator 430 includesa plurality of pixels 431. In such cases, providing the first light492-1 includes (operation 542) reflecting, at a first pixel of theplurality of pixels 431, at least a portion of the illumination light490 as the first light 492-1 while the first pixel is in a first state;and providing the second light 492-2 includes reflecting, at a secondpixel of the plurality of pixels 431, at least a portion of theillumination light 490 as the second light 492-2 while the second pixelis in a second state that is different from the first state. FIG. 4Ashows a pixel (e.g., pixel 431-7) providing the first light 492-1 andFIG. 4B shows the same pixel (e.g., pixel 431-7) providing the secondlight 492-2. Because each pixel 431 of the plurality of pixels isindividually activatable, the first pixel may be deactivated to providethe first light 492-1 and a second pixel different from the first pixelmay be activated to provide the second light 492-2 (or vice versa).

In some embodiments, each of the first direction and the seconddirection is determined (562) at least in part based on the refractiveindex of the transparent optical element 440 and the angle θ between thefirst surface 440-1 of the transparent optical element 440 and thesurface 430-1 or 430-2 of reflective spatial light modulator 430.

In some embodiments, the first direction corresponds (564) to a firstdiffraction order of the grating 420 and the second directioncorresponds to a zeroth diffraction order of the grating 420.

In some embodiments, the method 500 includes (operation 566) receivingthe second light 492-2 transmitted through the grating 420 at apolarizer 460, and transmitting the second light 492-2 having the secondpolarization through the polarizer 460.

In some embodiments, the method 500 includes (operation 568) receivingthe second light 492-2 at an output assembly 470.

In light of these principles, we now turn to certain embodiments ofdisplay devices.

In accordance with some embodiments, a display assembly (e.g., displayassembly 400) includes a light source (e.g., light source 410), agrating (e.g., grating 420), and a reflective spatial light modulator(e.g., reflective spatial light modulator 430). The light source isconfigured to emit illumination light (e.g., illumination light 490).The reflective spatial light modulator is configured to receive theillumination light and reflect at least a portion of the illuminationlight. The grating is positioned to (i) redirect the illumination lightoutput from the light source toward the reflective spatial lightmodulator, (ii) receive at least a portion of the reflected light fromthe reflective spatial light modulator, (iii) redirect first light(e.g., first light 492-1) having a first polarization toward the lightsource, and (iv) transmit second light (e.g., second light 492-2) havinga second polarization through the grating. The second polarization isorthogonal to the first polarization.

In some embodiments, an optical surface (e.g., surface 420-1 or 420-2)of the grating (e.g., grating 420) is non-parallel and non-perpendicularto a surface (e.g., surface 430-1 or 430-2) of the reflective spatiallight modulator (e.g., reflective spatial light modulator.

In some embodiments, the display assembly (e.g., display assembly 400)further includes a transparent optical element (e.g., transparentoptical element 440) that has a first surface (e.g., first surface440-1) and a second surface (e.g., second surface 440-2) that isnon-parallel to the first surface and parallel to a surface (e.g.,surface 430-1 or 430-2) of the reflective spatial light modulator (e.g.,reflective spatial light modulator 430). The grating (e.g., grating 420)is disposed on the first surface (e.g., first surface 440-1) of thetransparent optical element.

In some embodiments, the transparent optical element (e.g., transparentoptical element 440) is disposed between the grating (e.g., grating 420)and the reflective spatial light modulator (e.g., reflective spatiallight modulator 430). The transparent optical element has a refractiveindex that is different from the refractive index of air. The firstsurface (e.g., first surface 440-1) of the transparent optical elementforms an angle (e.g., angle θ) with the surface (e.g., surface 430-1 or430-2) of the reflective spatial light modulator.

In some embodiments, the display assembly (e.g., display assembly 400)further includes an absorptive polarizer (e.g., polarizer 450) disposedbetween the light source (e.g., light source 410) and the grating (e.g.,grating 420) and configured to transmit illumination light (e.g.,illumination light 490) having the first polarization.

In some embodiments, display assembly (e.g., display assembly 400)further includes an output assembly (e.g., output assembly 470)configured to receive the second light (e.g., second light 492-2) outputfrom the grating (e.g., grating 420). The grating is disposed betweenthe reflective spatial light modulator (e.g., reflective spatial lightmodulator 430) and the output assembly.

In some embodiments, the display assembly (e.g., display assembly 400)further includes a polarizer (e.g., polarizer 460) configured totransmit the second light (e.g., second light 492-2) having the secondpolarization.

In some embodiments, the reflective spatial light modulator includes aplurality of pixels (e.g., pixels 431, including pixels 431-1, 431-2,431-3, . . . , 431-n) and a respective pixel (e.g., pixel 431-1) of theplurality of pixels is individually activatable. In some embodiments, arespective pixel of the plurality of pixels is configured to receive theillumination light (e.g., illumination light 490) having a firstpolarization (e.g., a first linear polarization) and provide (i) firstlight (e.g., first light 492-1) having the first polarization while therespective pixel is in a first state and (ii) second light (e.g., secondlight 492-2) having a second polarization that is orthogonal to thefirst polarization while the respective pixel is in a second state thatis different from the first state.

In some embodiments, the reflective spatial light modulator (e.g.,reflective spatial light modulator 430) includes a reflective surface(e.g., reflective surface 432), a quarter wave plate (e.g., opticalretarder 433), and a layer of optically anisotropic molecules (e.g.,layer of optically anisotropic molecules 434) disposed between thereflective surface and the quarter wave plate.

In some embodiments, the reflective spatial light modulator (e.g.,reflective spatial light modulator 430) is a liquid crystal optical onsilicon display (e.g., LCoS display).

In accordance with some embodiments, a method (e.g., method 500)includes (operation 510) receiving illumination light (e.g.,illumination light 490) having a first polarization at a grating (e.g.,grating 420), and (operation 520) redirecting, with the grating, theillumination light toward a reflective spatial light modulator (e.g.,reflective spatial light modulator 430). The method further includes(operation 530) receiving the illumination light redirected by thegrating at the reflective spatial light modulator, and (operation 540)providing, by the reflective spatial light modulator, first light (e.g.,first light 492-1) having the first polarization and second light (e.g.,second light 492-2) having a second polarization that is orthogonal tothe first polarization. The method further includes (operation 550)receiving the first light and the second light at the grating; and(operation 560) directing, with the grating, the first light toward afirst direction; and directing, with the grating, the second lighttoward a second direction that is different from the first direction. Insome embodiments, directing, with the grating, the second light towardthe second direction includes transmitting the second light through thegrating.

In some embodiments, the reflective spatial light modulator (e.g.,reflective spatial light modulator 430) includes a plurality of pixels(e.g., pixels 431, including pixels 431-1, 431-2, 431-3, . . . , 431-n).In some embodiments, providing the first light (e.g., first light 492-1)includes (operation 542) reflecting the illumination light (e.g.,illumination light 490) as the first light at a first pixel (e.g., afirst pixel 431-1) of the plurality of pixels (e.g., pixels 431) whilethe first pixel is in a first state, and (operation 552) providing thesecond light (e.g., second light 492-2) includes reflecting theillumination light as the second light at a second pixel (e.g., secondpixel 431-2) of the plurality of pixels while the second pixel is in asecond state that is different from the first state.

In some embodiments, the method (e.g., method 500) further includes(operation 502) outputting initial light (e.g., initial light 489) froma light source (e.g., light source 410), (operation 502) receiving theinitial light at an absorptive polarizer (e.g., polarizer 450) andtransmitting, through the absorptive polarizer, at least a portion ofthe initial light having the first polarization as the illuminationlight (e.g., illumination light 490).

In some embodiments, method (e.g., method 500) further includes(operation 504) outputting the illumination light (e.g., illuminationlight 490) from a light source (e.g., light source 410). Additionally,the grating (e.g., grating 420) may be disposed between the light sourceand the reflective spatial light modulator (e.g., reflective spatiallight modulator 430).

In some embodiments, the method (e.g., method 500) further includes(operation 566) receiving the second light transmitted through thegrating at a polarizer, and transmitting the second light having thesecond polarization through (e.g., by) the polarizer.

In some embodiments, the method (e.g., method 500) further includes(operation 568) receiving the second light (e.g., second light 492-2) atan output assembly (e.g., output assembly 470).

In some embodiments, an optical surface (e.g., surface 420-1 or 420-2)of the grating (e.g., grating 420) is non-parallel and non-perpendicularto a surface (e.g., surface 430-1 or 430-2) of the reflective spatiallight modulator (e.g., reflective spatial light modulator 430). Forexample, as shown in FIGS. 4A-4C, an optical surface of the gratingforms an angle (e.g., angle θ) with respect to a surface of thereflective spatial light modulator.

In some embodiments, the grating (e.g., grating 420) is disposed on afirst surface (e.g., first surface 440-1) of a transparent opticalelement (e.g., transparent optical element 440). The transparent opticalelement has a second surface (e.g., second surface 440-2) that isnon-parallel to the first surface and parallel to a surface (e.g.,surface 430-1 or 430-2) of the reflective spatial light modulator (e.g.,reflective spatial light modulator 430). For example, as shown in FIGS.4A-4C, the first surface of the transparent optical element forms anangle (e.g., angle θ) with respect to the second surface of thetransparent optical element.

In some embodiments, (operation 518) the transparent optical element(e.g., transparent optical element 440) is disposed between the grating(e.g., grating 420) and the reflective spatial light modulator (e.g.,reflective spatial light modulator 430). The transparent optical elementhas a refractive index that is different from the refractive index ofair, and the first surface (e.g., first surface 440-1) of thetransparent optical element forms an angle (e.g., angle θ, and acuteangle) with the surface (e.g., surface 430-1 or 430-2) of the reflectivespatial light modulator. Each of the first direction and the seconddirection is determined at least in part by the refractive index of thetransparent optical element and the angle between the first surface ofthe transparent optical element and the surface of reflective spatiallight modulator.

In some embodiments, as shown in FIG. 4C, the reflective spatial lightmodulator (e.g., reflective spatial light modulator 430) includes areflective surface (e.g., reflective surface 432), a quarter wave plate(e.g., optical retarder 433), and a layer of optically anisotropicmolecules (e.g., layer of optically anisotropic molecules 434) that isdisposed between the reflective surface and the quarter wave plate.

Although various drawings illustrate operations of particular componentsor particular groups of components with respect to one eye, a personhaving ordinary skill in the art would understand that analogousoperations can be performed with respect to the other eye or both eyes.For brevity, such details are not repeated herein.

Although some of various drawings illustrate a number of logical stagesin a particular order, stages which are not order dependent may bereordered and other stages may be combined or broken out. While somereordering or other groupings are specifically mentioned, others will beapparent to those of ordinary skill in the art, so the ordering andgroupings presented herein are not an exhaustive list of alternatives.Moreover, it should be recognized that the stages could be implementedin hardware, firmware, software or any combination thereof.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the scope of the claims to the precise forms disclosed. Manymodifications and variations are possible in view of the aboveteachings. The embodiments were chosen in order to best explain theprinciples underlying the claims and their practical applications, tothereby enable others skilled in the art to best use the embodimentswith various modifications as are suited to the particular usescontemplated.

What is claimed is:
 1. A display assembly, comprising: a light sourceconfigured to emit illumination light; a reflective spatial lightmodulator configured to receive the illumination light and reflect atleast a portion of the illumination light; and a grating positioned to:redirect the illumination light output from the light source toward thereflective spatial light modulator; receive at least a portion of thereflected light from the reflective spatial light modulator; redirectfirst light having a first polarization toward the light source; andtransmit second light having a second polarization orthogonal to thefirst polarization through the grating.
 2. The display assembly of claim1, wherein an optical surface of the grating is non-parallel andnon-perpendicular to a surface of the reflective spatial lightmodulator.
 3. The display assembly of claim 1, further comprising atransparent optical element having a first surface and a second surfacethat is non-parallel to the first surface and parallel to a surface ofthe reflective spatial light modulator, and the grating is disposed onthe first surface of the transparent optical element.
 4. The displayassembly of claim 3, wherein: the transparent optical element isdisposed between the grating and the reflective spatial light modulator;the transparent optical element has a refractive index that is differentfrom a refractive index of air; and the first surface of the transparentoptical element forms an angle with the surface of the reflectivespatial light modulator.
 5. The display assembly of claim 1, furthercomprising an absorptive polarizer disposed between the light source andthe grating and configured to transmit illumination light having thefirst polarization.
 6. The display assembly of claim 1, furthercomprising an output assembly configured to receive the second lightoutput from the grating, wherein the grating is disposed between thereflective spatial light modulator and the output assembly.
 7. Thedisplay assembly of claim 6, further comprising a polarizer configuredto transmit the second light having the second polarization.
 8. Thedisplay assembly of claim 1, wherein: the reflective spatial lightmodulator includes a plurality of pixels; and a respective pixel of theplurality of pixels is individually activatable.
 9. The display assemblyof claim 1, wherein the reflective spatial light modulator includes areflective surface, a quarter wave plate, and a layer of opticallyanisotropic molecules disposed between the reflective surface and thequarter wave plate.
 10. The display assembly of claim 1, wherein thereflective spatial light modulator is a liquid crystal optical onsilicon display.
 11. A method, comprising: receiving illumination lightat a grating; redirecting, with the grating, the illumination lighttoward a reflective spatial light modulator; receiving, at thereflective spatial light modulator, the illumination light redirected bythe grating; providing, by the reflective spatial light modulator, firstlight having a first polarization and second light having a secondpolarization that is orthogonal to the first polarization; receiving thefirst light and the second light at the grating; directing, with thegrating, the first light toward a first direction; and directing, withthe grating, the second light toward a second direction that isdifferent from the first direction.
 12. The method of claim 11, furthercomprising: outputting initial light from a light source; receiving theinitial light at an absorptive polarizer; and transmitting, through theabsorptive polarizer, at least a portion of the initial light having thefirst polarization as the illumination light.
 13. The method of claim11, further comprising: outputting the illumination light from a lightsource, wherein the grating is disposed between the light source and thereflective spatial light modulator.
 14. The method of claim 11, furthercomprising: receiving, at a polarizer, the second light transmittedthrough the grating; and transmitting, through the polarizer, the secondlight having the second polarization.
 15. The method of claim 11,further comprising: receiving the second light at an output assembly.16. The method of claim 11, wherein: the reflective spatial lightmodulator includes a plurality of pixels; providing the first lightincludes reflecting, at a first pixel of the plurality of pixels, atleast a portion of the illumination light as the first light while thefirst pixel is in a first state; and providing the second light includesreflecting, at a second pixel of the plurality of pixels, at least aportion of the illumination light as the second light while the secondpixel is in a second state different from the first state.
 17. Themethod of claim 11, wherein an optical surface of the grating isnon-parallel and non-perpendicular to a surface of the reflectivespatial light modulator.
 18. The method of claim 11, wherein: thegrating is disposed on a first surface of a transparent optical element;and the transparent optical element has a second surface that isnon-parallel to the first surface and parallel to a surface of thereflective spatial light modulator.
 19. The method of claim 18, wherein:the transparent optical element is disposed between the grating and thereflective spatial light modulator; the transparent optical element hasa refractive index that is different from a refractive index of air; thefirst surface of the transparent optical element forms an acute anglewith the surface of the reflective spatial light modulator; and each ofthe first direction and the second direction is determined at least inpart by the refractive index of the transparent optical element and theangle between the first surface of the transparent optical element andthe surface of the reflective spatial light modulator.
 20. The method ofclaim 11, wherein the reflective spatial light modulator includes areflective surface and a layer of optically anisotropic moleculesdisposed over the reflective surface.